Various chemical compounds of interest, such as biofuels like fatty acid esters or alcohols, functional foods, vitamins, pharmaceuticals such as lactams, peptides and polyketides or terpenes and terpenoids and also biopolymers such as polyhydroxyalkanoates can be produced via metabolically enhanced cyanobacteria. One of these compounds is ethanol. In this context, the PCT patent application WO 2009/098089 A2 discloses the use of ethanologenic genes, for example pyruvate decarboxylase and alcohol dehydrogenase for the production of ethanol.
Typically, the cyanobacterial host cells for the production of a specific chemical compound of interest are metabolically enhanced hybrid lines, which have been transformed with genetic elements containing corresponding production genes under the control of either constitutive or inducible promoters. In the case of inducible promoters, transcription of the production genes is coupled to specific induction conditions, for instance the addition or depletion of certain metals such as Cu, Zn etc. to, or from, the culture medium.
It is a known problem in the art that such metabolically enhanced cyanobacteria produce such chemical compounds, e.g. ethanol, for a certain period of time, before the productivity decreases due to mutations in the respective production genes. For example, Takahama and colleagues (2003) investigated the time-related productivity of a recombinant Synechococcus elongatus PCC 7942 harboring a heterologous gene for an ethylene-forming enzyme. They found that the rate of ethylene production in the recombinant culture decreased as a result of competition with faster growing ethylene-non-forming mutants that carried short nucleotide insertions within the coding sequence of the gene for the ethylene forming enzyme.
Therefore, there is a need for improved cyanobacterial hybrid strains for prolonged production of first chemical compounds.
This task is solved by providing a metabolically enhanced cyanobacterium according to base claim 1. Further claims are directed to advantageous embodiments of the metabolically enhanced cyanobacteria, to a method of producing the metabolically enhanced cyanobacteria, and to a method of producing a first chemical compound by culturing the metabolically enhanced cyanobacteria.